1. Field of the Invention
This invention relates to a diversity glass antenna for an automobile which is suitable for receiving a radiowave of approximately 30 MHz through 3 GHz.
2. Description of the Prior Art
As shown in FIG. 24, conventionally, a glass antenna is mounted on an automobile on sale and is publicly known, wherein a main antenna 31 and a subantenna 32 are provided on the upper portion and the lower portion of a glass plate 1 in a rear window of an automobile, interposing a defogger composed of bus bars 5 and a plurality of heater lines 2. In this case, to perform diversity receiving, receiving signals of the main antenna 31 and the sub antenna 32 are inputted into a selecting circuit 11 and a stronger one of the receiving signals is selected and transmitted to a receiver.
However, in the conventional example, since the main antenna 31 and the sub antenna 32 are single pole antennas, that is, antennas each of which employs a potential difference between a single power feeding point and the ground as the receiving signal, the directivity characteristics of both are similar. As a result, it is possible to adjust the antennas to be omni-directional with respect to a polarization plane in a specific direction. However, it is not possible to adjust the antenna to be omni-directional with respect to all the polarization planes and the diversity effect can not be provided.
Furthermore, when the receiving is performed by a single omni-directional antenna, irrespective of a pole antenna or a glass antenna, a multiple path strain is generated by simultaneously receiving the original radiowave and a reflecting wave from a building or the like and the receiving sound quality is deteriorated.